Buoyancy Calculator
Buoyancy is the upward push a fluid gives anything placed in it. It depends on how much fluid is pushed aside, not on how heavy the object is, which is why a steel ship floats and a steel nail does not.
Buoyant force
490.5
- Object weight
- 294.3
- Net upward force
- 196.2
- Volume submerged when floating
- 60.00%
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
buoyant force = fluid density x displaced volume x gravity
- F
- Buoyant force pushing upwards, in newtons
- rho
- Density of the fluid, about 1000 kilograms per cubic metre for water
- V
- Volume of fluid displaced, in cubic metres
- g
- Acceleration due to gravity, about 9.81 metres per second squared
How to check the result by hand
- 1
Find the submerged volume
In cubic metres. Fifty litres is 0.05 cubic metres, and for a floating object only the part below the surface counts.
- 2
Look up the fluid density
Fresh water is about 1000 kilograms per cubic metre, sea water about 1025, and air about 1.2. The fluid, not the object, sets this number.
- 3
Multiply density by volume by gravity
One thousand times 0.05 times 9.81 gives about four hundred and ninety newtons of upward force.
- 4
Work out the object's weight
Mass times gravity. A thirty kilogram object weighs about two hundred and ninety four newtons, which is less than the lift available, so it floats.
- 5
Compare the two to get the net force
Four hundred and ninety minus two hundred and ninety four leaves about one hundred and ninety six newtons upwards, and the object floats with sixty per cent of its volume submerged.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Buoyancy page.